MQTT
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Định nghĩa
Giao thức Truyền tải Đo xa Hàng đợi Tin nhắn (Message Queuing Telemetry Transport). Giao thức nhắn tin xuất bản-đăng ký nhẹ được thiết kế cho thiết bị hạn chế và mạng băng thông thấp. Được sử dụng rộng rãi trong IoT để thu thập dữ liệu cảm biến và điều khiển thiết bị.
Publish-Subscribe for Constrained Devices
MQTT (Message Queuing Telemetry Transport) is a lightweight publish-subscribe protocol designed for IoT devices operating over unreliable, low-bandwidth networks. Devices publish messages to a broker on named topics; other devices subscribe to topics and receive messages asynchronously. This decoupling means a temperature sensor doesn't need to know who is consuming its readings — it just publishes to sensors/building-a/floor-3/temperature.
QoS Levels and Retained Messages
MQTT defines three Quality of Service levels over TCPTransmission Control Protocol. A reliable, connection-oriented transport protocol that guarantees ordered, error-checked delivery of data through three-way handshakes, acknowledgments, and retransmission. The foundation of HTTP, SSH, and most internet services.:
| QoS | Guarantee | Use Case |
|---|---|---|
| 0 | At most once (fire and forget) | Frequent, lossy telemetry |
| 1 | At least once (may duplicate) | Commands that must arrive |
| 2 | Exactly once (no duplicates) | Billing, inventory updates |
A retained message is stored by the broker and immediately delivered to new subscribers — useful for device state that must be available on connection.
Security Considerations
MQTT over plain TCP (port 1883) transmits credentials in cleartext. Production deployments must use MQTT over SSL/TLSSecure Sockets Layer / Transport Layer Security. Cryptographic protocols that provide encrypted, authenticated communication over a network. SSL is deprecated; modern implementations use TLS 1.2 or TLS 1.3. (port 8883). Authentication is typically username/password; more secure deployments use client certificate mutual TLS. CoAPConstrained Application Protocol. A lightweight RESTful protocol designed for resource-constrained IoT devices, running over UDP with optional DTLS encryption. Similar to HTTP in design but optimized for low-power, lossy networks. serves a similar niche for REST-style IoT communication, while AMQPAdvanced Message Queuing Protocol. An open standard for message-oriented middleware that provides reliable, asynchronous message delivery with features like queuing, routing, and publish-subscribe. Used by RabbitMQ and Azure Service Bus. provides stronger enterprise messaging guarantees. Because many IoT brokers are internet-accessible, IP Blacklist Check should be used to audit broker IP reputation before exposing a broker endpoint publicly.